Reducing the overall power consumption is a key factor in ensuring proper operation of a wide gamut of electronic components and devices.
For instance, a micro-controller can save power while it is not operating, by staying in one of its low power modes (WAIT, HALT, ACTIVE HALT). In the low power modes, the micro-controller switches off the core, the embedded oscillators, the memories, the analog macro cells and/or the gating clock to the peripherals. When a routine is to be executed, the micro-controller can be “awoken” from an external/internal interrupt. After executing the routine, the micro-controller can return to one of its low power modes until a new request arrives.
Typically, the higher is the power consumption reduction in the selected state, the longer is the time required to wake up the micro-controller from the low-power mode. To reduce the micro-controller power consumption, it is also useful to switch the internal clock controller to a low-power/low-frequency oscillator. When the micro-controller is fed with this low frequency oscillator source, the system is working in a SLOW mode. In this SLOW mode the micro-controller is still operating: the core and the other parts of the micro-controller are active but fed with a low-frequency clock thus reducing power consumption.
While operating, a micro-controller is able to access the embedded non-volatile memory in order to fetch, decode, and execute the instructions of a program. When the micro-controller is fed with a low-power/low-frequency oscillator and is working in the SLOW mode, the memory is still consuming power because the memory is always ON. When the memory is accessed by the core, it consumes power for an entire clock cycle even it the time required to access the memory is lower.